On a domain like truecrypt.org, you cannot see the actual website trough https, but when you download the signatures of their files or their pgp key, they will send it to you through https. However firefox does not seem to give me the possibility to look at the certificate in this situation.

What is a practical way of looking at the certificate, preferably without having to install extra tools...

How are you downloading the signatures, through Firefox or another tool? Also, are you wanting to view the certificate of the signature you've downloaded? Please clarify your question.
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ultrasawbladeNov 17 '11 at 20:06

@ultrasawblade You can view SSL certificate information by clicking the publisher's name on the left of the address bar and then selecting More information…. It looks like this. But for this to work in Firefox, you need to have an actual web page open.
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Daniel Beck♦Nov 17 '11 at 20:12

Im sorry, im not very good at formulating well, but i have specifically included the link so you can see for yourself. the files like signatures and their pgp key are on their download page.
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ufotdsNov 17 '11 at 20:23